This invention relates to methods and compositions suitable for removing the discolorations on hard surfaces caused by water borne manganese ions. These dicolorations are particularly evident on hard surfaces associated in automatic dishwashing when detergent compositions containing chlorinating compounds are used in conjunction with water containing manganese ions.
Detergent compositions containing chlorinating compounds are now widely used for many cleansing applications. It has been observed for some time that metallic surfaces such as gold, silver, platinum and certain nonmetallic surfaces including chinaware, glass, porcelain and plastic, and those surfaces such as are found inside automatic dishwashing machines and other similar household appliances become discolored when contacted with detergent formulations containing chlorinating agents in the presence of manganese ions. Additionally, the same manganese ion discoloration has been found to occur on the surfaces of swimming pools when certain oxidizing agents, as previously discussed, are employed for treating the pool water. This discoloration is particularly noticed when the aforementioned elements are brought together at elevated temperatures as those usually associated with washing appliances. Since the water of many communities contains sufficient concentrations of manganese ions to cause discoloration of hard surfaces, it is apparent that a serious problem exists in this regard.
The discoloration, previously referred to, occurs usually in the presence of manganese ions when halogenating or other oxidizing compounds are present. The rate at which the discoloration appears is associated with the relative amounts of manganese ion and oxidizing compound present. The staining is particularly rapid when the oxidizing agent is present at the levels associated with the use of a commercial chlorinated dishwasher product.
The following halogenating compounds have been found to induce discoloration: sodium and potassium dichloroisocyanurate, dichloroisocyanuric acid, trichloroisocyanuric acid, dichlorodimethylhydantoin, N,N-dichloro-p-toluene-sulfonamide, sodium chlorite and chlorine. These compounds, in the presence of manganese ion bearing water, will cause discoloration when used alone or when incorporated into detergent compositions. Elemental bromine has also been found to cause discoloration of hard surfaces in like manner.
While the aforementioned compounds are all nonalkaline halogenating agents, it should not be inferred that the discoloration will not occur in the presence of alkaline chlorinating agents. To the contrary it has been found that the discoloration is also caused when alkaline chlorinating compounds are present along with the water borne manganese ions. Typical examples of these compounds include: calcium and sodium hypochlorite and chlorinated trisodium phosphate.
While the aforementioned examples produce the characteristic stain under the previously outlined conditions, it is not to be implied that the discoloration will occur only with these particular agents. In actuality, the discoloration of the hard surface will occur with any agent sufficiently strong to oxidize manganese ions. What should be noted, however, is that both elements; the manganese ions and the oxidizing agent must be present. Thus when either manganese ions or the oxidizing materials are removed, it is observed that no discoloration occurs.